When vehicles become weapons

Transforming a vehicle into a simple but deadly weapon of terror -- as happened to such bloody effect in Nice on Thursday -- is a tactic well known to intelligence agencies.

A truck smashed into revellers celebrating France's Bastille Day, killing at least 80 and injuring scores as its ploughed two kilometres through the crowd.

Western authorities have had to deal with three similar attacks in recent years: two in Britain and another in Canada.

In May 2013, two Islamists smashed their car into British soldier Lee Rigby before attempting to behead him on a London street in broad daylight.

The pair, who were of Nigerian heritage, said they attacked the 25-year-old fusilier to avenge the deaths of Muslims at the hands of British troops.

Just 18 months later, a man claiming to be acting in the name of radical jihad ran over and killed Canadian soldier Patrice Vincent, also injuring a second man.

Shortly after, the 25-year-old Muslim convert, Martin Couture-Rouleau, called the police emergency line to dedicate his attack to the cause of jihad.

And in June 2007, two men in a burning jeep smashed into the main terminal building at Scotland's Glasgow Airport. One of the men was jailed for life, with the judge describing him as a "religious extremist".

For several years, extremist groups such as Islamic State and Al-Qaeda have exhorted followers via videos or messages to carry out such attacks using whatever comes to hand.

In September 2014, Abu Mohammed al-Adnani, an IS spokesman who Western intelligence agencies have dubbed the group's "attacks minister", issued chilling instructions that some have since apparently followed.

"If you cannot (detonate) a bomb or (fire) a bullet, arrange to meet alone with a French or an American infidel and bash his skull in with a rock, slaughter him with a knife, run him over with your car, throw him off a cliff, strangle him, or inject him with poison," he said.

Al-Adnani said there was no need to "consult anyone" as all unbelievers are fair game: "It is immaterial if the infidel is a combatant or a civilian... They are both enemies. The blood of both is permitted."